National Park Time-Critical Human Health Risk Assessment

Terraphase conducted a preliminary human health risk assessment for a National Park site. The assessment was performed to address concerns about potential human exposures to site-related contamination from former cattle ranch operations. The evaluation focused on volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), pesticides, and metals in the soil.

Scope of Services

Using conservative exposure assumptions and fate and transport models, Terraphase assessed potential health risks from exposure of park visitors, employees, and visiting scholars to site-related contamination in the soil. The project consisted of conducting soil sampling and performing a risk evaluation at key areas of a former cattle ranch, applying conservative exposure assumptions and fate and transport modeling, to estimate cumulative cancer risk and noncancer hazards. The risk assessment demonstrated that chemicals in soil would not pose an unacceptable risk to human health, and that the park could be opened to visitors, park employees and visiting scholars.

Notable Accomplishments

• Completed a comprehensive risk assessment in less than 20 days
• Confirmed that risks to receptors would not exceed risk management thresholds, demonstrating that it was safe to reopen the park
• Enabled the park to confidently restore public access

Planned Residential Development Vapor Intrusion Risk Assessment

Terraphase provided comprehensive human health risk assessment (HHRA) support for a large planned residential development in southern California. Groundwater contamination emanating from a closed municipal waste landfill posed a potential threat to the development via vapor intrusion.

Scope of Services

Terraphase developed a detailed hydrogeologic conceptual site model (CSM) and completed two HHRAs. These efforts guided the investigation, evaluation, and decision-making process regarding the need for engineering controls to mitigate vapor intrusion exposures prior to construction. Key activities included characterizing the site’s subsurface conditions, assessing cancer risks and noncancer hazards to future residents, and supporting the incorporation of vapor intrusion mitigation systems only where necessary.

Notable Accomplishments

• Vapor intrusion modeling and risk assessments provided a reliable scientific basis for determining which specific homes required vapor mitigation systems, which optimized both safety and cost-effectiveness of the development
• Ensured the safe and sustainable development of the residential community while effectively collaborating with, and enhancing the services of, other engineering and environmental consulting firms, as well as the client’s legal counsel, to achieve the client objectives

Wetlands Baseline Ecological Risk Assessment

Terraphase performed an ecological risk assessment (ERA) to support a brownfield investigation and feasibility study for the revitalization of a historically impacted wetland area in Delaware. The developer’s vision is to transform the site into a restored habitat that delivers ecological and community benefits.

Scope of Services

Using state, regional, and federal guidelines, the ERA evaluated potential risks to terrestrial plants and invertebrates, rooted aquatic plants, benthic invertebrates, fish, birds, and mammals. Exposure was estimated to contaminants in soil, sediment, and surface water. Of the dozens of chemicals analyzed, only 10 were identified as chemicals of potential ecological concern (COPECs).

Following the initial screening, a baseline ecological risk assessment (BERA) evaluated the COPECs more comprehensively using receptor-specific thresholds and food chain modeling.

American robin, short-tailed shrew, muskrat, spotted sandpiper, great blue heron, and largemouth bass were selected as receptors representing different feeding guilds (e.g., herbivores, invertivores, omnivores) and exposure media. Metals were identified as the primary risk drivers (i.e., chemicals of ecological concern [COEC])for all receptors, except the short-tailed shrew for which high molecular weight polycyclic aromatic hydrocarbons (PAHs) were also identified.

Using the results of the BERA, risk-based preliminary remediation goals (PRGs) were developed to support remedial planning and designs. Regional background concentrations for metals were also taken into consideration when selecting the PRGs.

Following review by the Delaware Department of Natural Resources and Environmental Control (DNREC), the outcome of the BERA and the resulting PRGs will be used in a feasibility study for focused remediation and redevelopment of the site into a community asset.

Notable Accomplishments

• ERA was conducted per state, regional, and federal guidance for multiple ecological receptors
• Contaminant exposure assessed in soil, sediment, and surface water
• Ten COPECs were identified from dozens of chemicals analyzed
• BERA was completed using receptor-specific thresholds and food chain modeling
• Metals were identified as primary COECs
• Risk-based PRGs were developed to support remedial planning
• BERA and PRGs to inform feasibility study for focused remediation, and community-focused site redevelopment, following DNREC review